1. Field of the Invention
The present invention relates to the preparation of polyisocyanato-polyisocyanurates by the partial catalytic cyclotrimerization of polyisocyanates, with the reaction subsequently being deliberately terminated when the proportion of trimer reaches the desired value. This invention more especially relates to the method of deactivating the catalyst, when employing a catalyst compound comprising an aminosilyl function.
2. Description of the Prior Art
Numerous catalysts are known to this art which make it possible to cyclotrimerize aliphatic or aromatic polyisocyanates to give polyisocyanato-polyisocyanurates. Each catalyst used is subsequently deactivated by a suitable technique appropriate to the particular catalytic agent used.
It is known, for example, to carry out the partial cyclotrimerization of simple aliphatic or aromatic polyisocyanates or of polyisocyanate adducts with the aid of basic catalysts, such as tertiary amines (German Patent No. 951,168), alkali metal or alkaline earth metal derivatives, such as hydroxides, carbonates, alcoholates and the like (French Patent No. 1,190,065), quaternary ammonium hydroxides (French Patent Nos. 1,204,697 and 1,566,256; European Patent Applications Nos. 3,765 and 10,589), catalysts containing an ethyleneimine group (French Patent Nos. 1,401,513 and 2,230,642) and finally, Mannich bases generally obtained from phenol, aldehyde and secondary amine (French Patent Nos. 2,290,459 and 2,332,274). These basic catalysts are, in general, quite naturally deactivated by the introduction of an acidic compound, such as an acid (phosphoric acid, hydrochloric acid, or the like). The catalytic activity of Mannich bases can also be destroyed either by a heat treatment or by the addition of an alkylating agent (dimethyl sulfate, methyl iodide, or the like).
Furthermore, it is also known to prepare polyisocyanoto-polyisocyanurates by catalytic cyclotrimerization using phosphines as catalysts (French Patent Nos. 1,510,342 and 2,023,423; published German Patent Application No. 1,934,763). In general, the deactivation of the phosphines after the cyclotrimerization reaction is effected by the addition of an alklyating or acylating agent, or alternatively by the addition of sulfur.
Under industrial conditions, the method of terminating the catalytic cyclotrimerization reaction is of very great importance. In destroying the catalyst, the deactivator (together with the destroyed catalyst) will end up, after conversion, in the polyisocyanato-polyisocyanurate in the form of more or less complex "moieties" which, however, will unavoidably have a sometimes considerable influence on the coloration of the product, its stability, and the like.
In addition, acidic agents are corrosive towards the equipment used on the industrial scale, both for manufacture and for storage.
Furthermore, a new catalyst system has now been developed making it possible to cyclotrimerize aliphatic or cycloaliphatic polyisocyanates to give polyisocyanato-polyisocyanurates, such polyisocyanates being simple polyisocyanates or polyisocyanate adducts. Thus, the use of compounds containing aminosilyl groups as catalysts, such as monoaminosilanes, diaminosilanes, silylureas and silazanes, makes it possible to carry out the cyclotrimerization reaction without an induction period and in a uniform manner at a relatively moderate temperature, which very greatly reduces the formation of dimeric polyisocyanate. These catalysts, which will be specified in the description to follow, are described in French Patent Applications 81/02,192 and 81/23,135, assigned to the assignee hereof, and hereby expressly incorporated by reference. In these patent applications, it was indicated that the catalyst was deactivated by the addition of an acidic compound, such as a strong acid or an acid halide. It was noticed, however, that the use of these deactivators resulted in a few disadvantages (coloration, corrosion, possible catalytic effect of the corrosion products, and so forth).